In the oil and gas industry, elements that are attached to a downhole tubular body, for example to a production tubing, are used for a number of purposes. An example of such elements is so-called stabilizers or centralizers placed externally on the tubular body. The purpose of a stabilizer may be to ensure that a downhole unit is stabilized centrally in a surrounding tubular body. On casing, for example, stabilizers are used as spacers ensuring sufficient radial spacing between two casings, so that the introduction of cement is done in a satisfactory way. For other downhole units, stabilizers may be used to reduce the radial movement, especially for long, slim units like bottom-hole assemblies (BHA), for example. In one embodiment, the stabilizers are fixedly arranged on the jacket surface of a relatively short mandrel which, when necessary, is slipped over the tubular body, which is to be equipped with stabilizers, and attached there. The stabilizers may exhibit a wide variety of shapes; both straight and helical stabilizer elements are well known in the trade. Stabilizer assemblies of this kind, termed stabilizer pipes in the further description, may be floatingly arranged on the downhole body, that is to say they are fixed only axially on the downhole unit so that the stabilizer pipe may rotate on the downhole unit and thereby be stationary when the downhole unit rotates, the axial fixing being provided by means of stop sleeves that are attached to the downhole unit by shrinking, pressing, screws and so on. In other applications, the stabilizer pipe is fixed in a rotationally rigid manner to the downhole unit in order to follow as the downhole unit rotates. The attachment is carried out in the same manner as that mentioned for the stop sleeves. An attachment of this kind may require large and expensive tools, and some of the attachment methods, for example pressing, often cause lasting deformation of the contact surfaces of the relevant downhole unit.
Stabilizers and centralizers are also found as pipe sections which are mounted in the pipe string in need of stabilization (stabilizer sub) by the pipe section being provided, at its ends, with threaded portions corresponding to the threaded portions of the adjacent pipes. This invention does not relate to this form of stabilizers and centralizers.
Other examples of elements that require attachment to a downhole tubular body are sand filters in a production tubing and conduits arranged externally on the production tubing for conveying control signals, hydraulic fluid and so on.